1. Field of the Invention:
This invention relates to gas turbine generation systems, and more particularly provides systems utilizing multiple heating stages including direct firing between the turbine compression and expansion stages.
2. Description of the Prior Art:
Present gas turbine technology can permit the use of relatively high turbine expander inlet temperatures, up to 1425.degree. K. for base load applications. However, heat exchanger technology practically limits gas inlet temperatures to about 1075.degree. K. Advanced designs have been proposed which could increase heat exchanger discharge temperatures to about 1275.degree. K., but which still would not match the gas turbine performance potential.
To obtain higher expander inlet temperatures, components imparting heat to the expansion medium have been interposed between the compression and expansion stages. For example, it is known to heat the compressed oxidant in a convective air heater and subsequently a coal fired atmospheric fluidized bed combustor, prior to entry into the expander. In such systems gaseous products discharged from the fluidized bed combustor are directed to the convective air heater. Exhaust from the expander is directed to the fluidized bed as a heating and fluidizing gas. While such systems increase the expander inlet temperature, the increase does not take full advantage of the expander capability.
It is therefore desirable to provide gas turbine generation systems which allow utilization of the full capability of a modern gas turbine expander.